Transformer Secondary

Status
Not open for further replies.
W

websparky

Senior Member
Location
Cleveland, Ohio
Here is a job I am reviewing on Monday.
I am looking for your input so I can compare it to my notes and the specs on the drawing. I have left out certain info on purpose as to not distract from the code issues. Please give me your opinon.
Thanks!
trfr.jpg
 
Re: Transformer Secondary

Originally posted by websparky:
Here is a job I am reviewing on Monday.
I am looking for your input so I can compare it to my notes and the specs on the drawing. I have left out certain info on purpose as to not distract from the code issues. Please give me your opinon.
Thanks!
trfr3.jpg
 
Re: Transformer Secondary

IMO Whatever combination of OCPDs is used the safe bet is to limit the total to 521 amps.

150 kVA @ 208 = 416 * 1.25 = 521 amps.

Note 2 of Table 450.3(B)
2. Where secondary overcurrent protection is required, the secondary overcurrent device shall be permitted to consist of not more than six circuit breakers or six sets of fuses grouped in one location. Where multiple overcurrent devices are utilized, the total of all the device ratings shall not exceed the allowed value of a single overcurrent device. If both breakers and fuses are utilized as the overcurrent device, the total of the device ratings shall not exceed that allowed for fuses.
Click to expand...
But this same transformer could be protected with a single 600 amp breaker, so perhaps the total of the three OCPDs should be 600 amps?
 
Re: Transformer Secondary

The panels need main breakers to satsify 408.36. These could be 225A for each, per the rating of the panels. To determine the conductor size, we need to know the length of the secondary circuits.

EDIT: The more I think about it, the less sure I am! :)

[ January 08, 2006, 04:51 PM: Message edited by: ryan_618 ]
 
Re: Transformer Secondary

art. 450 protects the transformer, art. 240 protects the conductors, look at art. 240.21, you cannot not tap a tap.
 
Re: Transformer Secondary

Originally posted by mpd:
art. 450 protects the transformer, art. 240 protects the conductors, look at art. 240.21, you cannot not tap a tap.
Click to expand...
mdp you can install up to six secondary Overcurrent devices at a transformer.

That is not in dispute.
 
Re: Transformer Secondary

Originally posted by ryan_618:
The panels need main breakers to satsify 408.36. These could be 225A for each, per the rating of the panels. To determine the conductor size, we need to know the length of the secondary circuits.

EDIT: The more I think about it, the less sure I am! :)
Click to expand...
It is a 'thinker' isn't it.

With three 225s the total secondary protection 675 amps would be way to high for the 150 kVA

[ January 08, 2006, 04:55 PM: Message edited by: iwire ]
 
Re: Transformer Secondary

iwire

the plan shows tapping the 600 kcmil, that is a violation of 240.21
 
Re: Transformer Secondary

Originally posted by mpd:
iwire

the plan shows tapping the 600 kcmil, that is a violation of 240.21
Click to expand...
How do you know that?

Do you know what size conductors are running to each panel?

Check the definition of tap. ;)
 
Re: Transformer Secondary

I am just reading what is on the plan, there is only 4 600 kcmil and says 600"s tapped here
 
Re: Transformer Secondary

Originally posted by mpd:
I am just reading what is on the plan, there is only 4 600 kcmil and says 600"s tapped here
Click to expand...
Yes it does, and Dave was also asking what size those conductors to the panels would have to be.

It looks like they will all have to be the same size as the ones from the transformer to the gutter.

The only times I seen more than one OCPD for a transformer each OCPD had it's own set of conductors to the transformer terminals.
 
Re: Transformer Secondary

Bob,
Article 450 does not enter into the answer to this question. All of the requirements of that article are statisified by the 200 amp OCPD on the primary. The only question here is the taps on the secondary conductors. I see nothing in the code that would permit the installation as shown. It needs either a single OCPD before the 225 amp panels or individual sets of secondary conductors from the transformer to the panels.
Don
 
Re: Transformer Secondary

iwire

the last sentence you just wrote is exactly what I am saying, the way that plan is, it is a violation of 240.21
 
Re: Transformer Secondary

Originally posted by don_resqcapt19:
Bob,
Article 450 does not enter into the answer to this question. All of the requirements of that article are statisified by the 200 amp OCPD on the primary.
Click to expand...
DOH!

I understand that...now. :eek: Thanks.

I do not see why you do not think it could be done if we do not 'tap a tap'. :confused:
 
Re: Transformer Secondary

I was wrong about it all.

I took a minute stepped away from the NEC on disc and went to my 2005 book. I find it easer to apply Charlie's rules when I read from paper.

MDP you where right.

Don....well... heck you are almost always right.

Really blew this one. :eek:

Oh well live and learn. :cool:

Bob
 
Re: Transformer Secondary

Originally posted by websparky:
Bob,
Please tell us what the options are for this install! It is confussing :)
Click to expand...
Hey I already have a size 11 firmly planted in my mouth :eek: , I am going to go lick my wounds.

About the only thing I got right was that it is a 'thinker'.

So far I have learned forget 450 and forget about any kind of tap.

[ January 08, 2006, 06:08 PM: Message edited by: iwire ]
 
Re: Transformer Secondary

OK, here is one proposed otion:

The overall length of the secondary conductors is less than 25'. Install a 125A and 2 150A main breakers in the 3 panels and tap the 600kcmil with the wire rated for each breaker.

Would this work?
 
Re: Transformer Secondary

websparky

no that would be a violation of 240.21

iwire

if we all are not learning, we are not living.
 
Re: Transformer Secondary

MPD help me nail down were in 240.21 you can not tap here is it that it dose not say you can tap a secondary
 
Status
Not open for further replies.
Top